The diagnosis and/or treatment of disease in nuclear medicine constitute one of the major applications of short-lived radioisotopes. It is estimated that in nuclear medicine over 90% of diagnostic procedures performed worldwide annually use 99mTc labelled radio-pharmaceuticals. Given the short half-life of diagnostic radio-pharmaceuticals, it is helpful to have the facility to generate suitable radioisotopes on site. Accordingly, the adoption of portable hospital/clinic size 99mTc generators has greatly increased over the years. Portable radioisotope generators are used to obtain a shorter-lived daughter radioisotope which is the product of radioactive decay of a longer-lived parent radioisotope, usually adsorbed on a bed in an ion exchange column. Conventionally, the radioisotope generator includes shielding around the ion exchange column containing the parent radioisotope along with means for eluting the daughter radioisotope from the column with an eluate, such as saline solution. In use, the eluate is passed through the ion exchange column and the daughter radioisotope is collected in solution with the eluate, to be used as required.
In the case of 99mTc, this radioisotope is the principle product of the radioactive decay of 99Mo. Within the generator, conventionally the 99Mo is adsorbed on a bed of aluminium oxide and decays to generate 99mTc. As the 99mTc has a relatively short half-life it establishes a transient equilibrium within the ion exchange column after approximately twenty-four hours. Accordingly, the 99mTc can be eluted daily from the ion exchange column by flushing a solution of chloride ions, i.e. sterile saline solution through the ion exchange column. This prompts an ion exchange reaction, in which the chloride ions displace 99mTc but not 99Mo.
In the case of radio-pharmaceuticals, it is highly desirable for the radioisotope generation process to be performed under aseptic conditions i.e. there should be no ingress of bacteria into the generator. Moreover, due to the fact that the isotopes used and generated with the generator are radioactive, and are thereby extremely hazardous if not handled in the correct manner, the radioisotope generation process also should be conducted under radiologically safe conditions. Naturally, it is desirable to ensure that when the elution process is performed, the radiological safety of the generator is not compromised. In particular, when the eluate is introduced into the generator, it is important for the radiological safety of the generator to be maintained.
In trying to ensure adequate radiological protection, some known radioisotope generators have tended to be of a complicated construction incorporating a large number of components. However, the radiological protection afforded by such structures can be compromised where the interconnection of the various components is unreliable. Such complex structures also add to the cost of the generator. It is thus important that the actual construction of the generator is reliable and all component interconnections are secured to a high degree of certainty.
U.S. Pat. No. 3,946,238 describes a shielded radioisotope generator comprising a cylindrical shielded housing for a central repository. The repository is bound by a removable top cover and side walls and a base which are made from lead and which act as the shielding. Within the repository a bottle is located which contains an ion exchange column in which 99Mo is absorbed. When it is desired to add saline solution to the system to prompt the elution of 99mTc, the top cover is removed, and the saline is introduced by way of a transfer pipette. The saline solution is introduced by means of the pipette to an annular region between the bottle and the inner surfaces of the shielding. From this annular region the saline solution flows in a controlled manner into the bottle containing the ion exchange bed via a series of radial openings in the wall of the bottle. The transfer pipette has a long handle designed such that a user's hands always remain outside the generator when saline is introduced into the annular region about the bottle. It is apparent, however, that the removal of the top cover for the purposes of introducing the saline solution constitutes an unacceptable radiological risk as the interior of the repository is radioactive.
U.S. Pat. No. 3,564,256 describes a radioisotope generator having quick-coupling members for the elution process. The generator includes a cylindrical holder containing a radioactive substance bound to an ion exchange bed. The holder is closed by rubber plugs at both ends, and is surrounded by shielding having passages opposite each of the rubber plugs in which respective needles are located. At the outermost ends of the needles quick-coupling members are provided to enable a syringe vessel containing a saline solution to be quickly and easily connected to one of the needles and to enable a collection vessel to be connected to the other of the two needles. In use, each one of the rubber plugs of the cylindrical holder is pierced by one of the needles to prompt the elution of 99mTc from the ion exchange column. Suitable quick-coupling members proposed in the document are conventional detachable injection needle to injection syringe connections.
U.S. Pat. No. 4,387,303 describes a radioisotope generator comprising a column having an elute inlet aperture and an elute outlet aperture and containing an ion exchange bed with the parent radioisotope. Both the elute inlet and outlet are in communication with channels in the surrounding shielding. One of the channels, that is in communication with the elute outlet, is connected to a tapping point on the generator via an eluate conduit. The tapping point is adapted to receive an evacuated elution vial for collection of the daughter radioisotope in solution and consists of a hollow needle that pierces the seal to the evacuated elution vial. The eluate conduit is also in communication with a source of sterile air and the generator includes a device for interrupting the elution process before the elution vial is filled by interrupting the flow of sterile air. No information is provided with regard to the construction of the generator and in particular no information is provided as to how the hollow needle at the tapping point is held in position.